Last month, Margo bought a tree that grows $2.5 \text{ cm}$ each day. It was $5 \text{ cm}$ tall when she bought it and now it is $65 \text{ cm}$ tall. Write an equation to determine the number of days $(d)$ Margo has owned the plant. Find the number of days Margo has owned the plant.
Answer: Let $d$ be the number of days Margo has owned the plant. The plant was $5 \text{ cm}$ tall when Margo purchased it. During the $d$ days she has owned the plant it has grown $2.5d \text{ cm}$. The current height of the plant is $5+2.5d$. Since the current height of the plant is $65 \text{ cm}$, let's set this equal to $65$ : $ 5+2.5d=65$ Now, let's solve the equation to find the number of days $(d)$ Margo has owned the plant. $\begin{aligned} 5+2.5d&=65\\ \\ 5+2.5d{-5}&=65{-5}&&{\text{subtract }5} \text{ from each side}\\ \\ 2.5d&=60\\ \\ \dfrac{2.5d}{{2.5}}&=\dfrac{60}{{2.5}}&&\text{divide each side by ${2.5}$}\\ \\ d&=24\end{aligned}$ The equation is $5+2.5d=65$. Margo has owned the plant for $24$ days.